The invention relates to a transmission system comprising at least a transmitter and a receiver for transmitting data formatted in blocks over a transmission channel which introduces a distortion which is defined on the basis of multiplicative coefficients, said receiver comprising block detection means for detecting blocks by successive iterations, said block detection means themselves comprising block multiplier means for multiplying blocks via a filter matrix intended to compensate for said distortion.
The invention also relates to a receiver intended to be used in such a system, a block detection method intended to be used in such a receiver and a computer program for implementing such a method.
The invention finds important applications in the field of transmissions by a channel subjected to fading, for example, a Rayleigh channel or a Rice channel. This is the case, for example, with mobile radio systems and mobile satellite transmission systems.
A transmission system of this type is notably described in the article xe2x80x9cTransformation of a Rayleigh fading channel into a set of parallel AWGN channels and its advantages for coded transmissionxe2x80x9d by M Reinhardt and J. Lindner, published in Electronics Letters vol. 31, no. 25, Dec. 7, 1995.
In the system described in this article, the received blocks are multiplied via a filter matrix whose elements are written as       ρ    j    *              E      ⁢              xe2x80x83            ⁢              (                  ρ          j          2                )              +          N      0      
where xcfx81j*, j=1, . . . , M are the conjugates of the coefficients xcfx81j of the channel, M is the size of the block, E(xcfx81j2) is the likelihood of xcfx81j2 and No is the variance of the Gaussian noise.
In practice, this system has good performance for QPSK modulations. But the performance is insufficient for the QAM modulations and for PSK modulations which have a large number of points.
It is an object of the invention to propose a transmission system of the type defined above having better performance.
This object is achieved with a system as described in the opening paragraph and characterized in that the elements of the filter matrix are formed from a module power of said coefficients, the value of said power being a function of the iteration.
The values of said powers are chosen, for example, by applying an error minimization criterion.
In a first embodiment the number of iterations is fixed. In a second embodiment the detector or block detection means comprises means for determining the convergence of the decisions which are obtained at successive iterations, and means for terminating the detection when the convergence is determined. This second embodiment permits on average to limit the number of iterations necessary to come close to the performance obtained with a Gaussian channel (that is to say, a channel that is not subjected to fading).